Typical behaviour of a woman her age. I don't mean that in a mean way but we see a lot of elderly female patients where I work and this kind of behaviour is the norm really. We just take a deep breath and remember that they are 85 and that we will be the same way at that age. I doubt your MIL will be able to understand your condition. I am sure that she is really a nice intelligent woman but once people get into their 80's and 90's it can be very difficult.
I don't mean this to be nasty towards your MIL. But people in this age group tend to become very self centered, demanding and impossible to reason with. I looked after a 101 year old that is sharp as a knife and sweet as sugar the other day though.
I know I sound awful but I speak from experience.
Example: A 35 bedded ward with mostly elderly ladies and a 25 year old girl was really really unwell and went into cardiac arrest , stopped breathing and was dying. Two nurses on the ward and no other staff. Both nurses are trying to pound on the chest of the dying woman and get an airway in and call the crash team.
The 90 year olds in the next beds complained at all the "noise" which was "too much for them" then walked around the curtain where the nurses were doing CPR demanding cups of tea and commodes and some quiet.
When they were told that the only nurses were in the middle of a life and death emergency they became abusive and complained that they are being ignored and demanded that the nurses stop what they are doing and give them what they want.
They would not get out of the way and go back to their chairs and one grabbed the arm of one of the nurses as she was trying to do chest compressions. The nurses didn't bat an eyelash because this behaviour is so typical. They complained the rest of the night about all the "noise" and "commotion" and how the mean nurses made them wait. The family of the young patient was hysterical and the elderly patients complained at the noise...shouting "shut up" to these people.
Most of these women have varying degrees of dementia/confusion so it's not their fault that they are like this. Point is to forget trying to reason with this age group if you are in an emergency situation where you need to act fast.